The present invention relates to aqueous cationic surfactant formulations, to a process for their preparation and to their use.
Cationic surfactants are sought-after compounds which are used for numerous applications and are described in a large number of publications and patents. For example, DE-A 34 17 646 and DE-A 27 10 468 describe quaternary ammonium compounds as the most important representatives of the cationic surfactants, such as cetyltrimethylammonium chloride or stearyltrimethylammonium chloride, for use in hair after treatment compositions. A disadvantage when using these cationic surfactants is that they have a strong corrosive effect.
EP-B-0 098 802 describes the preparation of quaternary ammonium compounds, for example cetyldimethyl-2-hydroxyethylammonium dihydrogen phosphate with ethylene oxide in the presence of acids, preferably phosphoric acid, and the use of these cationic surfactants in hair cosmetics. Like the abovementioned compounds, these surfactants are easily frozen out of the solutions. Consequently, they have to be dissolved and homogenized before use. Alternatively, they have to be stored in special storage tanks such that they are unable to freeze out. Both measures entail additional costs.
DE-A 31 16 087 describes a process for preparing quaternary ammonium compounds from a tertiary amine and epoxides in the presence of quaternary ammonium compounds as catalyst. This method can be used to prepare cationic surfactants such as 2-hydroxyhexadecyl-2-hydroxyethyldimethylammonium chloride. These compounds too are easily frozen out and have a corrosive effect.
Cationic surfactants are required to have a range of advantageous properties. Examples of important requirements made of such surfactants are
1. good solubilization,
2. good compatibility with anionic surfactants,
3. good foam stabilization,
4. little or no corrosive effect,
5. good biocidal action,
6. good stability on storage,
7. no freezing out from the surfactant solution,
8. absence of halogen,
9. good conditioning effect,
10. good wetting, emulsifying and dispersing capacity, and
11. ease of preparation.
It is an object of the present invention to develop a cationic surfactant which provides as many as possible of these advantageous properties without having the disadvantages of the cationic surfactants known to date. We have found that this object is achieved by the aqueous cationic surfactant formulations of the invention, comprising in solution
a) from 10 to 50% by weight of a quaternary ammonium compound of the formula I: 
xe2x80x83where:
R1, R2, R3 and R4 independently are substituted or unsubstituted, branched or unbranched C1-C4- or substituted or unsubstituted, branched or unbranched, saturated or unsaturated C8-C16-alkyl, at least one and not more than two of R1, R2, R3 and R4 being substituted or unsubstituted, branched or unbranched, saturated or unsaturated C8-C16-alkyl, and a water-soluble anion of the Formula (II) is R5xe2x80x94Oxe2x80x94SO3xe2x80x94, where R5 is C1-C4-alkyl,
b) from 0.01 to 15% by weight of an amine of the Formula III: 
where R1, R2 and R3 are as defined above and not more than two of R1, R2 and R3 are substituted or unsubstituted, branched or unbranched, saturated or unsaturated C8-C16-alkyl, and
c) from 0.1 to 5.0% by weight of a buffer which maintains a pH in a range from 4 to 9.
In the formulae I and III R1, R2, R3 and R4 ind ependently are substituted or unsubstituted, branched or unbranched C1-C4-alkyl or substituted or unsubstituted, branched or unbranched, saturated or unsaturated C8-C16-alkyl, it being possible for at least one and not more than two, of R1, R2, R3 and R4 to be substituted or unsubstituted, branched or unbranched, saturated or unsaturated C8-C16-alkyl and advantageous definitions being as follows:
C1-C4-alkyl branched or unbranched C1-C4-alkyl chains such as methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl or 1,1-dimethylethyl, preferably methyl or ethyl;
C8-C16-alkyl: branched or unbranched, saturated C8-C16-alkyl chains such as n-octyl, 2-methylheptyl, 3-methylheptyl, 4-methylheptyl, 2,2-dimethylhexyl, 2,3-dimethylhexyl, 2,4-dimethylhexyl, 2,5-dimethylhexyl, 3,3-dimethylhexyl, 2,2,3-trimethylpentyl, 2,2,4-trimethylpentyl, 3,3,2-trimethylpentyl, 3,3,4-trimethylpentyl, 4,4,2-trimethylpentyl, 4,4,3-trimethylpentyl, 2,3,4-trimethylpentyl, 2-ethylhexyl, 3-ethylhexyl, n-nonyl, 3-ethyl-2-methylhexyl, 2-methyloctyl, 4-methyloctyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, 3-ethyl-5-isopropyl-4-methyloctyl, n-pentadecyl, n-hexadecyl, or branched or unbranched unsaturated C8-C16-alkyl chains, for example branched or unbranched C8-C16-alkenyl chains such as 1-octenyl, 2-octenyl, 3-octenyl, 4-octenyl, 5-octenyl, 6-octnyl or 7-octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, n-pentadecenyl, or n-hexadecenyl; preference is given to saturated and unsaturated alkyls or alkenyls which can be derived from amines of fatty alcohols such as caproyl alcohol, enanthyl alcohol, caprylyl alcohol, pelargonyl alcohol, capryl alcohol, lauryl alcohol, myristyl alcohol, pentadecanol, or cetyl alcohol, or amines of linear Ziegler alcohols (amination of the alcohols to the amine); particular preference is given to saturated C12-16-alkyl chains and very particular preference to saturated C12-C14-alkyl chains which can be prepared on the basis, for example, of coconut oil or palm kernel oil. Advantageous branched alkyls can be prepared, for example, on the basis of alcohols from the Guerbet reaction or the oxo reaction.
Examples of substituents of R1, R2, R3 and R4 are alkyl, hydroxylalkyl or hydroxylalkyl ether radicals.
R5 in the formula II is, advantageously, substituted or unsubstituted, branched or unbranched C1-C4-alkyl such as methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, or 1,1-dimethylethyl, preferably methyl or ethyl. Suitable substituents of R5 are alkyl, hydroxyalkyl or hydroxyalkyl ether radicals.
The content of quaternary ammonium compounds (a) of the formula I is in a range from 10 to 50% by weight, preferably from 15 to 40% by weight and, with particular preference, from 20 to 35% by weight, based on the overall weight of the surfactant formulation. Particularly preferred cationic surfactants in the surfactant formulation of the invention are surfactants having only one C8-C16-alkyl chain, preferably a C12-C16-alkyl chain and, with particular preference, with a C12-C14-alkyl chain, as in N,N,N-trimethyl-C12/C14-ammonium methyl sulfate.
The content of amines (b) of the Formula II is in a range from 0,01 to 15 % by weight, preferably from 0,1 to 10 % by weight and, with particular preference, from 0.5 to 5 % by weight, based on the overall weight of the surfactant formulation. Particularly preferred amines in the surfactant formulation of the invention are those having a long C8-C16-alkyl chain, preferably with a C12-C16-alkyl chain and, with particular preference, with a C12-C14-alkyl chain and two short C1-C4-alkyl chains, such as N,N-dimethyl-C12/C14-amine.
It has been found that by adding the buffer to the surfactant solution it is possible to bring about a marked improvement in the stability of the surfactant solution on storage without affecting the surfactant activity. Furthermore, it has likewise been possible to bring about a marked improvement in the solubilizer effect of the surfactant solution by adding the buffer.
The surfactant formulations of the invention comprise advantageously from 0.1 to 5.0% by weight, preferably from 0.5 to 4% by weight, and, with particular preference, from 1.0 to 3.5% by weight of buffer (c) based on the overall weight of the surfactant formulation.
Suitable buffers for the aqueous cationic surfactant formulations of the invention are in principle all those known buffers which maintain a pH in a range from 4 to 9, preferably from 5 to 8 and, with particular preference, from 6 to 8, as described, for example, in Handbook of Biochemistry (Eds. Sober, H. A., Horte R. A., The Chemical Rubber Co., 1968: J-195-J-199).
Examples of suitable buffers are all salts of weak acids and strong bases or of strong acids and weak bases, which can be salts of the same acids and bases or mixtures of different acids or bases.
Suitable examples of buffers are those such as Walpole buffer (acetic acid/Na acetate), Gomori aconitate buffer (aconitic acid/NaOH), Kolthoff buffer (borax/succinate), Sxc3x6rensen""s citrate II buffer (disodium citrate/NaOH), McIlvaine""s Citric acid/phosphate buffer (citric acid/disodium phosphate), Stafford, Watson and Rand""s dimethylglutaric acid buffer (dimethylglutaric acid/NaOH), Sxc3x6rensen""s phosphate buffer (potassium/dihydrogen phosphate/disodium hydrogen phosphate), Gomori trismaleate buffer (trismaleate/NaOH) or Gomori succinate buffer (succinate/NaOH). Other suitable buffers include MES, ADA, PIPES, BIS-TRIS, MOPSO, BIS-TRIS PROPANE, MOPS, DIPSO, TAPSO, HEPPSO, POPSO, EPPS, TEA, TAPS or ACES, which are customary buffers in biochemistry, or amino acid buffers. Preference is given to buffers which can be prepared advantageously from weak acids and their salts, examples being sodium acetate/acetic acid, sodium citrate/citric acid, sodium borate/boric acid, sodium phosphate/phosphoric acid, potassium phosphate/phosphoric acid, hydrogen carbonate/soda, sodium hydroxide/citric acid, sodium hydroxide/tartaric acid or mixtures thereof. Further suitable buffers include cholamine chloride, BES, TES, HEPES, acetamidoglycine, glycinamide, tris, bicine, tricine, glycylglycine or buffers based on ethanolamine or diethanolamine.
Individual buffers or mixtures can be used in the surfactant formulation of the invention.
Particular preference is given to the use of buffers or buffer mixtures based on hydrogen phosphate/dihydrogen phosphate, such as sodium phosphate/phosphoric acid, potassium phosphate/phosphoric acid, disodium hydrogen phosphate/sodium dihydrogen phosphate, dipotassium hydrogen phosphate/potassium dihydrogen phosphate or KOH/H3PO4 or NaOH/H3PO4, since in addition to the advantageous effects mentioned above these are known to have a corrosion protection effect.
Another advantageous property of the surfactant formulations of the invention is excellent stability on cold storage; in other words, the formulations do not freeze out below 20xc2x0 C. Unlike the commercial products they show no precipitation or inhomogeneity below this temperature. This is due firstly to the preferred length of the longer alkyl chains of C8-C16, where the proportion of the C16-alkyl chain within the alkyl chain distribution should be as low as possible, and secondly to the buffer. With high proportions of C16-alkyl chains, the cold stability of the surfactant formulations of the invention may decrease.
The surfactant formulations of the invention may if desired comprise further additives or auxiliaries known to the skilled worker, such as electrolytes for increasing the viscosity, sodium chloride or other customary salts, hydroxyalkylcellulose, cationic celluloses, cationic synthetic polymers, other cationic surfactants, such as Dehyquart(copyright) grades or Luviquat(copyright) grades, alkyl ether sulfates or alkyl polyglycosides, or may if desired be combined with further surfactants, for example with cationic or anionic surfactants.
The surfactant formulations of the invention can be synthesized by a range of methods known to the skilled worker, for example using alkylating agents such as alkyl sulfates, alkylsulfonates, alkyl halides or other active esters based on various amines as starting substances; advantageously, the process of the invention is used for the synthesis.
The process of the invention which has been found for preparing compounds of the formula I comprises reacting amines of the formula III 
in aqueous solution with a dialkyl sulfate of the formula IV 
where R1 to R5 are as defined above in a molar ratio range from 85 to 99.99 mol % based on the amine and at from 20 to 100xc2x0 C. and then adding to the reaction solution from 0.1 to 5.0% by weight of a buffer which maintains a pH in a range from 4 to 9.
In the process of the invention the dialkyl sulfate is advantageously used in a molar ratio of from 85 to 99.9 mol %, preferably from 95 to 99.5 mol %, and with particular preference, from 97.0 to 99.0 mol % based on the amine (=100 mol %), so that there is always an excess of amine and so that the monoalkyl sulfate formed in the reaction is present in the surfactant formulation in no more than equimolar amounts with respect to the quaternary ammonium compound that is formed.
The reaction is advantageously carried out at from 20 to 100xc2x0 C., preferably from 40 to 90xc2x0 C. and, with particular preference from 50 to 80xc2x0 C.
The alkylation can be conducted with or without pH control; in the former case, by adding sodium or potassium hydroxide solution, for instance. It is preferred not to control the pH. The sodium or potassium hydroxide solution added if pH control is carried out can advantageously later become a constituent of the buffer.
In the process of the invention it is advantageous to react an initial charge of aqueous alkylamine solution, emulsion or suspension with the dialkyl sulfate which is metered in. The metered addition of the dialkyl sulfate is in this case advantageously controlled such that the abovementioned temperature ranges are not exceeded. In principle, it is also possible to have the dialkyl sulfate as the initial charge and to meter in the alkyl amine, or to conduct the reaction in the mixing chamber with simultaneous addition of the reactants. In order to facilitate rapid addition of the dialkyl sulfate the reaction is advantageously conducted with cooling and under inert conditions, although cooling is generally not necessary.
In a preferred embodiment, the buffer can be added after alkylation to the reaction solution, it being possible for the buffer to be produced in the solutionxe2x80x94which is preferredxe2x80x94or else to be added as a ready-made buffer to the reaction solution. The buffers can be used in the form of solutions or as solids. In principle the buffer can be added before, during or after the alkylation reaction, the latter being preferred.
The cationic surfactant formulations of the invention are suitable for a range of applications, preferably for cosmetics, for example in cosmetic formulations having care and/or conditioning properties, examples being styling products such as hair mousses, hair gels or hairsprays or after treatment compositions such as hair lotions, treatment rinses, treatment packs, treatment fluids for damaged ends, hair repair compositions, hot oil treatments, shampoos, liquid soaps or beauty creams.
The surfactant formulations are suitable as hydrophobicizers, as antistats, for coating textiles or leather, as electroplating auxiliaries, as metal cleaning assistants, as corrosion inhibitors, as flocculants or coagulants, as textile printing auxiliaries, for printing inks and printing plates, as dispersants for paints and coatings, as auxiliaries for the electrical and electronics industry, as biocides and as constituents of disinfectants, as pharmaceutical auxiliaries or for animal cosmetics. The surfactant formulations of the invention are also suitable as initiators for cationic polymerization, as polymerization media or as binders for bitumen.